About Haman the Agagite
Haman (Also known as Haman the Agagite המן האגגי, or Haman the evil המן הרשע) was Vizier to King Xerxes (AKA Ahasuerus) of the the Persian empire. He is the main antagonist in the Book of Esther, As his name indicates, Haman was a descendant of Agag, the king of the Amalekites, a people who were wiped out in certain areas by King Saul and David, by God's command.
The Book of Esther tells how Haman and his wife Zeresh instigate a plot to kill all of the Jews in the Persian Empire. The plot is foiled by Queen Esther, the king's recent wife, who is herself a Jew. Haman is hanged from the gallows that he himself had built to hang his worst enemy, Mordechai. Having foiled the plot, the Jews proceed to kill the enemies who had planned on killing them, including the 10 sons of Haman. They then hung his sons from a gallows (Esther 9:5-14).